User:EnthusiasticGeek/Keyboard Case

So far, these are my personal observations of the PinePhone Keyboard. The name of that will change -- oops.

This Keyboard Case is a case for the PinePhone and PinePhone Pro. As the name implies, it adds a keyboard to the phones. It also has a 6000 mAh battery that essentially tripples the phone's 3000 mAh battery life.

Connectivity

The Keyboard Case has six pins that connect it to the PinePhone or PinePhone Pro.

INT  SDA  SCL
VBUS VBAT GND

• The SDA and SCL pins are connected to the PinePhone or PinePhone Pro's I2C bus. This is how the phone and keyboard communincate.
• VBUS connects to the USB +5V line. See Charging Information for more information
• The VBAT pin connects to the battery. This powers the keyboard if it is out of power.
• INT is a pin that's used for interrupts. In the case of the preinstalled firmware , it is used so the phone can request key presses from the keyboard.

Charging Information

In most schematics, including the PinePhone and PinePhone Pro, the usually +5V coming from the usb connector is named VBUS. This voltage is fed into the System-On-a-Chip in the PinePhone (Allwinner A64) or PinePhone Pro (RK3399S). The SOC then manages this voltage and charges the battery.

The VBUS rail is also accessed through one of the pogo pins on the back of the phone. This is what the keyboard uses to charge the phone. The output of the IP5209 chip is connected to the VBUS rail through this pogo pin, which charges the phone. This makes the keyboard act as a USB charger with only +5V and GND connected, which charges the phone.

Problems with Charging Implimentation

This could change in the near future.

The way in which the PinePhone and PinePhone Pro can charge with the keyboard breaks the USB-C spec. When the keyboard charges the phone, the VBUS line is always putting out +5V. If the phone and connected device negotiates that the phone shall be the sink, or if the connected device does not have any negotiation capabilities and acts as a source (such as a simple charger), +5V will continue to be put out by the PinePhone or PinePhone Pro at the same time as the source is putting out +5V. This means that, for example, a charger plugged into the phone while the keyboard is connected may result in some unintended behavior.

In the case of the original PinePhone, this can be fixed by Pine64 by having the VBUS pin on the keyboard instead connect to the Allwinner A64's second power input, similar to how it's handled on the PineTab. However, the RK3399S used on the PinePhone Pro does not have this feature, which means it may not be as easily fixable on the it.

Resources

PinePhone (Pro) Keyboard Case on the official Pine Store

Pine64 Blog Post - January 1st 2022